Flag registers (assembly language) with types and examples

GENERAL PURPOSE & FLAG REGISTERS
Made by Asmita
Dept MCS
27/12/2017

REGISTERS IN COMPUTERS
To speed up the processor operations,
the processor includes some internal memory
storage locations, called registers.

Registers
Processing element
Main Memory
Address bus
Data bus
Control bus
WHY REGISTERS????

TYPES OF REGISTERS::
GGGU • S
General Purpose
Used for more than one
purpose.
1.AX Accumlator
2.BX Base
3.CX Count
4.DX Destination
X=SIZE
AH AL
Special Purpose
Used for only one purpose for which
they are made.
1.IP/(PC)= instruction pointer.
2.IR=instuction registers.
3.BP=base pointer.
4.SP=stack pointer.
5.SI=source index registers.
6.DI=destination registers.
7.CS= code segment registers.
8.DS=data segment registers
9.ES=extra segment registers
10.SS=stack segment registers.
AX

CPU word size/ CPU width
 Its mean how many NO. of bits that can be
processed by processor.

0 1 2 3 4 5
A
Base Registers = Starting Address

For(int i=0; i<10; i++)
Cout<<“welcome”;
Num1*Num2 = 38 bits answer

General purpose also uses
in
 Takes input.
 Display output.
 Stores intermediate results.

Flags  A flag is a piece of
fabric (most often
rectangular or
quadrilateral) with
a distinctive
design that is used
as a symbol, as a
signaling device,
or as decoration.

Carry flag
1
1100 1000 ax
+
1101 0010 bx
_________________
11101 1010
If there comes a carry then the value of carry flag
becomes 1
Otherwise 0

Parity flag
 Used for error detection and correction.
 To ensure that the received data is exactly as
it is as send data.

Regiters RAM
1 1 0 1 0 1 1 01 1 0 000
Due to voltage
Send data Lost /corrupt
P
0
Flag registerEVEN parity
If 1’s is even=0
If 1’s is odd=1

Auxilary flag
1 1
0100 1100
+
1100 1110
________________________
10001 1110

Zero flag
2
_
2
________
0
(here the value of zero register will be 1)
When the ans=0
Then the zero flag become 1
Otherwise 0.

Sign registers
2
+
-6
_________
4
6
+
2
_______
8
S
0
For positive value it
becomes=0
Otherwise=1

Trap flag
 Used to facilitate debugger.
 Executes each line of code, values in
variables.
 When trap flag =1,
 It Goes in single step execution mode.
 And tells which value is in variables, in
registers and all information.
_________________________
________________________
________________________

Interrupt flag
 A signal generated by h/w or s/w for getting CPU attention.
 If the value of interrupt register =1
 Than the CPU leave its work and works on interrupt.
 But if the value =0, then CPU Continue its own work and
ignores interrupt.
 Flag register
 Interrupt
I
1
CPU

Programmable Interupt Controller
PIC CPU
I
0
INTERRUPT
FLAG Register

Direction flag
 Tells us In which direction the processing of
string will happen?
 If the value of direction flag=0, then the string
processing starts from left to right.
 But if the value=1 , then its display the string
from high index to low index means from right to
left.
 “IloveAssembly”
 “ylbmessAevolI”

Overflow flags
 n1* n2= answer more than 16 bits.
 n1+n2= 17 bits.
 A register can store maximum 16 bits of data.
 So when the answer comes more than the 16 bit,
the execding data will be waste,
 So this register tells us that your data will be
waste and the value of overflow register
becomes =1
 Otherwise =0.

Flag registers (assembly language) with types and examples

Flag registers (assembly language) with types and examples

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Flag registers (assembly language) with types and examples